The invention relates to a method of correcting errors and erasures in digital information subdivided into code words in accordance with an error correction code with minimum distance d, which code words contain data symbols and redundant symbols, in theory it being possible to correct at the most Tmax errors, at the most T errors being corrected. The invention also relates to a device suitable for carrying out the method.
A method and device of the kind set forth are described in Philips Technical Review, Vol. 40, 1982, No. 6, pp. 166-173. Digital information representing, for example sound (sampled, quantized, coded and modulated audio signals) is subdivided into code words in conformity with an error correction code (for example, a Reed-Solomon code), which code words consist of data symbols (containing the actual information) and redundant symbols (added in accordance with the rules of the error correction code in order to enable error correction and detection). An incorrect symbol (i.e. a symbol to be corrected) whose position in the code word is known is referred to as an erasure. An incorrect symbol in a code word whose exact value and position in the code word are unknown, is referred to as an error. The term "error correction operation" may include the finding of the correct value of one or more erasure symbols. The error correction code used has a minimum distance, say d. In that case a number of t errors and a number of e erasures can be corrected per code word, provided that the equation 2t+e&lt; d is satisfied. The largest number of errors that can be corrected in theory, say Tmax, equals (d-1)/2 for d odd and (d-2)/2 for d even. Therefore, 2Tmax=(d-1)-(d-1)MODULO 2. The method utilizes known means (the input being the code word and erasure data, i.e. the number and the positions of the erasures in the code word) for correcting at the most T errors, the value of T being smaller than or equal to Tmax. The complexity of the means used for correcting at the most T errors (the known erco circuit) is highly dependent on the value of T, because the magnitude and difficulty of the calculations to be performed are a sharply rising function of T. Therefore, the means become very complex for high values of T.